In the last several years high optical power reliability in optical fiber and photonic components has become a major concern. This is due to the increasing output power of optical amplifiers in wavelength-division multiplexing systems and the advent of Raman amplification. Though today's C-band amplifiers are capable of launching more than 200 mW of C-band signal, the greatest concern now is in the area of Raman amplification where pump laser systems typically operate in the range of 1-2 W at about 1400 nm to about 1480 nm. When power this high is launched into transmission systems, it can cause long-term degradation of materials that can sometimes lead to catastrophic failure of a component, module, or the fiber itself.
A photothermal heating problem was recently discovered in a fiber re-coat material used to re-coat stripped regions at fusion splice joints of specialty dispersion compensating fibers used in a dispersion compensation module. In particular, a Raman-pumped module was constructed using a dispersion compensating fiber that was fusion spliced to a CS980 fiber (available from Corning Incorporated), and then re-coated with a standard ultraviolet curable urethane acrylate coating (Desolite 950-200, available from DSM Desotech Inc.). Due to the nature of the fiber, high splice losses of approximately 0.5-1.0 dB are common. These splice losses result in power being dumped into the cladding and then ultimately into the fiber re-coat material, where localized heating takes place. In the above-described Raman-pumped module, the module is expected to operate at 1.6 W at 1430-1480 nm, which means that even with the best splice losses achievable today as much as 180-330 mW of radiation can get dumped into the coating material and cause significant heating. In recent laboratory tests it was found that the Desolite 950-200 re-coated fiber splices can heat up to as much as 120-200° C. at 1.6 W of 1480 nm radiation. These temperatures will certainly cause long-term reliability problems with the coating and ultimately the fiber, if not short-term failure.
A similar problem of localized heating was also observed for coated optical fibers designed for high power applications of the type described above, but where the fibers were employed in environments requiring tight bends of the fiber (e.g., present in amplifier modules).
Though components in high power environments were the focus several years ago, today there is growing concern around the fiber and more particularly the fiber coating. It is known that organic materials can absorb radiation in the region of 1400-1620 nm due to vibrational overtones of the C—H, O—H, or N—H bonds commonly found in organic polymeric materials. As these bonds absorb energy, they heat and can cause thermal degradation of the coating. And if the coating integrity becomes compromised, the fiber will fail mechanically. From the foregoing, it should be appreciated that a need exists for optical fibers that can operate in high power applications without long-term or short-term failure caused by localized heating of the fiber coating.
The present invention is directed to overcoming these and other deficiencies in the art.